Notice that .
Can either 1 or 0 be included?
Let be the collection of closed intervals for . What do you notice about ? Is it closed, open, both, or neither?
I'm afraid the wording and available material has got me stumped on this, and being sick at the moment doesn't help.
EDIT: One more thing, I've looked at some work done on this in another forum, for which I will provide the link.
Is the work found here accurate?